How to Interpret Piping and Instrumentation Diagrams

With a bit of smoke, a few mirrors and a degree in hieroglyphics, anyone can learn to read a P&ID. Piping and Instrumentation Diagrams is a topic that can benefit process, project and design engineers, business developers, operators, safety, maintenance and even management.

Get a thorough explanation of symbology as it relates to Piping and Instrumentation-controls symbology, tag identification, I/O devices, valve symbol, primary flow element, horizontal line types, dashes, and more.

As I mentioned in Part 2, the meanings of the various symbols used on P&IDs (aka, symbology) are defined on separate drawings called “Lead Sheets” (or Legend Sheets). These are your “secret decoder rings” to P&ID symbology interpretation. Every company that builds process plants should have a set of lead sheets customized to their particular ways and means.

P&IDs may be viewed as a database of equipment, devices, lines and various sundry items that make up a process plant. Like a properly designed database, the tagging method employed on P&IDs needs to be robust and extensible. This Part 4 reviews key considerations and presents techniques that can be applied.

Learning to read and interpret piping and instrumentation diagrams via dry text-based articles (unlike those produced by yours truly) can be painful. To make this critical topic a bit more engaging, a series of videos intended to complement the series provided here are offered. They review the fundamentals of virtually every aspect of symbology and tag application.

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